Fluid is commonly pumped though tubing inserted into a well to drill or to provide intervention services such as stimulation or milling of obstructions. Means for pulsing this flow have been developed for a variety of applications, including mud pulse telemetry, well stimulation, enhanced drilling, and for use in extending the lateral range of drilling motors or other well intervention tools. For example, U.S. Pat. Nos. 6,237,701 and 7,139,219, which are assigned to the same assignee of the present invention, disclose hydraulic impulse generators incorporating self-piloted poppet valves designed to periodically stop the flow of fluid at the bottom end of the tubing. Stopping the flow leads to an increase in pressure upstream of the valve and a decrease in pressure downstream of the valve.
Pressure pulsations in the tubing disposed upstream of the bottom hole assembly (BHA) provide a plurality of beneficial effects. For example, the pulsations can improve the performance of rotary drilling by applying a cyclical mechanical load on the bit and a cyclic pressure load on the material that is being cut. In combination, these loads can enhance cutting. The vibrations induced by these cutting tools in the tubing can reduce the friction required to feed the tubing into long wells that deviate from a straight bore line.
The self-piloted poppet valve also generates pressure fluctuations in the wellbore near the tool. These pressure fluctuations can enhance chemical placement in the formation and enhance the production of formation fluids, such as oil or gas. In addition, the pressure pulses can also be used to generate a signal that can be employed for seismic processing.
The valve designs disclosed in U.S. Pat. Nos. 6,237,701 and 7,139,219 generate a relatively short pressure pulse, which limits pulse energy and effectiveness. These designs are also subject to relatively high differential pressure, which causes the tools to cycle at high speed, leading to wear and breakdown, and limiting the flow and pressure available to operate other tools, such as motors and jetting tools. The pulse amplitude generated by the hydraulic impulse tools is determined by the flow rate of fluid. An independent means for controlling pulse amplitude is required in order to accommodate the varying fluid flow rate requirements of a job, which may be determined by hole cleaning requirements in wells that deviate from a straight bore line, or by the limited size of tubing available for coiled tubing well intervention.
It would thus be desirable to increase the duration of the hydraulic impulse in order to increase impulse energy and effective range. It would further be desirable to reduce the pressure differential required to operate a hydraulic impulse generator. In addition, the cycle rate should be reduced to allow seismic interpretation and pore pressure prediction when the tools is used as a seismic source. Finally, it would be desirable to include means for controlling the impulse amplitude, while maintaining pulse duration and cycle rate.